The present invention relates to sprayable sunscreen compositions that are suitable for topical application to human skin and hair.
The damaging effects of sunlight on human skin have long been noted. In general terms, harmful ultra-violet (UV) rays, particularly those originating from sunlight, which penetrate the upper atmosphere and reach the earth's surface can be classified into two types: (i) high energy UV-B rays (290-320 nm wavelength) which are absorbed just above the dermis and are responsible for sunburn and tanning effects; and (ii) low energy UV-A rays (320-400 nm wavelength) which penetrate deeper into the skin (to the dermis and beyond), and which cause damaging effects that are more long term in nature, such as skin ageing.
Certain organic sunscreens composed of organic molecules that absorb the harmful ultra-violet rays have been proposed for use in mitigating the deleterious effects of ultra violet radiation. Organic sunscreen compounds which effectively absorb UV radiation in either the UV-A range or the UV-B range are known. However, a problem that exists with the organic sunscreens is that physiological damage to the body can occur following topical application of these sunscreens in quantities necessary to provide effective filtering of harmful ultra-violet radiation. As an alternative to organic sunscreens, certain inorganic substances such as titanium dioxide or zinc oxide which physically block exposure of the skin to ultra-violet rays have been employed.
A highly desirable method for delivering sunscreen compositions to the skin and hair is in the form of a finely dispersed spray. This form of product delivery offers improved product coverage on the skin or hair and allows easier application to difficult to reach areas. Such a spray is desirably delivered using a nonaerosol spray pump, which does not require the use of pressurized containers or special aerosolizing gases. The ability of such pump-driven delivery systems to deliver a product as a finely dispersed spray is critically dependent upon the viscosity of the composition at the exit port of the pump. As the viscosity of the composition decreases, the spray becomes more dispersed and yields a more desirable delivery. Conversely, as the viscosity increases, the spray becomes less dispersed and more stream-like, yielding a less desirable delivery.
It is well known in the art that stable oil-in-water emulsions are difficult to prepare at very low viscosities. Therefore, a need exists for stable oil-in-water compositions containing titanium oxide and/or zinc oxide, which have a high degree of stability and suspending power and yet are sufficiently thixotropic and low in viscosity that they can be effectively delivered to the skin or hair as fine spray using non-aerosol spray pumps.